The present invention relates to a process for producing formaldehyde from methyl chloride. A heterogeneous catalyst is used to oxidize methyl chloride with air to produce formaldehyde and hydrogen chloride. When integrated with technology for the manufacture of methyl chloride from methane and hydrogen chloride, the process of the present invention offers an independent source of formaldehyde.
Most of the world""s commercially produced formaldehyde is manufactured from methanol. Two processes are used to convert methyl alcohol to formaldehyde: one employs a silver catalyst and the other a metal oxide catalyst. A good review of these processes is provided by Kirk-Othmer, Encyclopedia of Chemical Technology, 4th ed., Volume 11, pages 935-939.
In the silver catalyst process, methyl alcohol and oxygen are passed through a silver gauze at 600xc2x0 to 650xc2x0 C. to produce formaldehyde by two simultaneous reactions, dehydration and oxidation. These reactions tend to balance each other, one being endothermic and the other exothermic. The overall yield, based on methanol, ranges from 88 to 92%.
The metal oxide catalyst process operates at significantly lower temperatures, 300xc2x0 C. to 400xc2x0 C., and provides yields between 92 and 95%. The main disadvantage of this process is that an excess of air is required to remove the substantial quantity of heat released by the oxidation reaction. This need results in a large volume of gases that must be treated.
Both commercial processes for the production of formaldehyde depend on methanol as the raw material. This restriction makes the economics of the processes sensitive to fluctuations in methanol pricing. Historically this dependence on methanol has resulted in considerable volatility in manufacturing cost.
The object of the present invention is to provide a process that overcomes the disadvantages of existing formaldehyde processes. Of primary concern is to free producers from their reliance on a single raw material.
In one particular embodiment of the invention, methyl chloride is oxidized with air over a catalyst to give formaldehyde and hydrogen chloride. After separating the hydrogen chloride from the reaction products, formaldehyde is obtained.
The catalyst used in the reaction to convert methyl chloride to formaldehyde may be of two forms. One type of catalyst consists of particles or pellets of uniform composition. The second type of catalyst is comprised of an intimate mixture of particles or pellets of two distinct compositions.
When a catalyst mix is used, the particles of one composition are designed to promote hydrolysis and the particles of the other composition function as a catalyst for oxidation. The proportion of the two different particles may be varied to control the rate of the reaction. Thus, within a catalyst mixture constituting the catalyst bed of a given reactor, a gradient may be established whereby the proportion of the oxidizing catalyst is greater at the inlet of the reactor than at the exit.
The reaction is carried out at a temperature in the range of approximately 250xc2x0 C. to approximately 400xc2x0 C. Close control of the temperature is desired in order to obtain maximum yields of product and to extend the life of the catalyst. The process is operated at essentially atmospheric pressure, but higher pressures up to about 10 bar may be employed to reduce the size of the equipment.